1. Field of the Invention
The present invention relates to an improvement in a bellows-like dust cover (boot) for protecting a shock absorber in an automobile suspension system against dust and muddy water.
2. Description of the Related Art
Many recent automobiles employ a strut suspension in which a shock absorber is used as a strut for wheel positioning. Such a strut suspension is comprised of a shock absorber and a coil spring positioned around the shock absorber. To protect the shock absorber against dust and muddy water, a dust cover is provided to extend around the shock absorber such that it covers the shock absorber over an area spanning from a piston rod portion to a body portion thereof with a given clearance between an outer periphery of the shock absorber and the dust cover. The dust cover has a bellows-like portion and is thus capable of telescopic action so that it can follow the telescopic action of the shock absorber.
The coil spring and dust cover are interrelated such that there should be formed a predetermined clearance between the dust cover and coil spring by the dust cover becoming larger in outer diameter when contracted. Whereas, for miniaturization of automobiles, such a clearance between the coil spring and dust cover should be kept to a minimum.
The bellows-like portion of such a conventional dust cover is comprised of a series of alternating ridges and grooves, the ridges being spaced apart at an equal pitch and having the same height. When blow molding the dust cover having such a complex portion, it is difficult to render it uniform in thickness at all portions thereof. Thus, the resulting dust cover may have weak and strong portions due to the thickness irregularities and is thus liable to experience buckling wherein the dust cover, when contracted, deforms to partially project laterally as shown in FIG. 8 hereof. This may give rise to such instances that when a coil spring extending around an outer periphery of the dust cover is compressed, the dust cover is pinched between adjacent two spirals of the coil spring, thus damaging the dust cover.
Improved dust cover is described in Japanese Utility Model Kokoku (Post-Exam) Publication No. SHO 63-27158 in which arrangements are made to prevent the aforementioned dust cover buckling. The bellows-like portion of the dust cover is comprised of a series of alternating ridges and grooves, the ridges having heights and pitches becoming small gradually from an upper end to a lower end of the dust cover and the grooves having substantially the same diameter. By virtue of the ridge heights and pitches becoming gradually small toward the lower end, contractive deformation takes place gradually from the upper to lower end of the dust cover so that its buckling can be kept to a minimum.
However, due to the bellows-like portion which is complicated in construction, difficulty is experienced in manufacturing the dust cover disclosed in Japanese Utility Model Post-Exam Publication No. SHO 63-27158. The dust cover is made from a rubber material by molding. For this molding, two metal molds are required which have grooves for forming the corresponding dust cover ridges having heights and pitches gradually becoming small toward the lower end thereof, as well as ridges for forming the corresponding dust cover grooves of substantially the same diameter. Manufacture of the metal molds with such complicated grooves and ridges is quite difficult and costly.